Apparatus, system and method for communicating a fault in a combination vehicle

ABSTRACT

Various embodiments of an apparatus, system and method for transmitting and indicating a fault in a combination vehicle are disclosed. A first towed vehicle controller comprises a processor with control logic capable of receiving fault messages and status messages on an associated vehicle communications bus; determining the status and faults of the first towed vehicle; and transmitting fault messages and status messages on the associated vehicle communications bus. When the control logic receives a fault message from an associated second towed vehicle controller on the associated vehicle communications bus at a second period in time, the control logic transmits the fault message of the associated second towed vehicle controller to the associated vehicle communications bus at a first period in time, different than the second period in time.

BACKGROUND

The present invention relates to an apparatus, a system and a method forcommunicating a fault in a combination vehicle. Commercial vehicles,such as long haul tractors, may be equipped to pull more than onetrailer. In some instances, a combination of three trailers and twodollies may be connected in series to the tractor to maximize the amountof cargo capable of being transported by the single tractor.

The tractor, trailers and dollies are required to be equipped withanti-lock braking systems (ABS). The power supply located on the tractoris generally connected in parallel with the trailers and dollies alonglong lengths of wire and multi-pin connectors at each portion of thecombination vehicle. The tractor, trailer and dollies are capable ofcommunicating among themselves using a power line carrier communicationsystem over the shared power supply wire. If there is a fault in atrailer or dolly ABS, the fault must be communicated to the tractor toinform the driver of the vehicle of the trailer ABS fault. In someinstances, the fault message from a trailer or trailers at the distalend of the combination vehicle will not be received by the tractor dueto message degradation over the length of wire, loading on the powerline, noise on the power line or other interference. There is a need foran improved method to communicate faults from a trailer or dolly to atractor in a combination vehicle.

SUMMARY

Various embodiments of an apparatus for communicating a fault in acombination vehicle are disclosed. In accordance with one example, afirst towed vehicle controller comprises an enclosure and a controllerin the enclosure. The controller comprises a processor with controllogic capable of determining at least one of a status and a fault of thefirst towed vehicle and transmitting fault messages and status messageson the associated vehicle communications bus and receiving faultmessages and status messages on an associated vehicle communicationsbus. When the control logic receives a fault message from an associatedsecond towed vehicle controller on the associated vehicle communicationsbus at a second period in time, the control logic transmits the faultmessage of the associated second towed vehicle controller to theassociated vehicle communications bus at a first period in time, whichis different than the second period in time.

In accordance with another example, a system for use in a combinationvehicle for communicating faults is disclosed. In accordance with oneexample, the system comprises a tractor controller in communication witha vehicle communications bus; a first towed vehicle controller incommunication with the vehicle communications bus and capable ofreceiving and transmitting messages to the vehicle communications bus;and a second towed vehicle controller in communication with the vehiclecommunications bus and capable of receiving and transmitting messages tothe vehicle communications bus. The first towed vehicle controllerdiscontinues transmitting a status message in response to receiving afault message from the second towed vehicle controller at a secondperiod in time and starts transmitting the fault message of the secondtowed vehicle controller to the vehicle communications bus at the firstperiod in time, which is different than the second period in time.

In accordance with another aspect, a method for communicating a fault isdisclosed. In accordance with one example, the method comprisesreceiving and transmitting messages on a vehicle communications busamong a first towed vehicle controller; a second towed vehiclecontroller and a tractor controller; transmitting a fault message fromthe second towed vehicle controller to the vehicle communications bus ata second period in time. The method further comprises receiving thefault message at the first towed vehicle controller on the vehiclecommunications bus and transmitting the fault message by the first towedvehicle controller at a first period in time, which is different thanthe second period in time.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which are incorporated in and constitute apart of the specification, examples of the invention are illustrated,which, together with a general description of the invention given above,and the detailed description given below, serve to exemplify theexamples of this invention.

FIG. 1 illustrates a schematic representation of a combination vehicleequipped with a system according to an example of the present invention.

FIG. 2 illustrates a schematic representation of the electrical systemof the combination vehicle shown in FIG. 1.

FIG. 3 illustrates a method of implementing the fault communicationsystem, according to an example of the present invention.

DETAILED DESCRIPTION

With reference to FIG. 1, a combination vehicle 10 is shown. Thecombination vehicle 10 comprises a tractor, or tractor 12. The tractor12 includes a tractor controller 14, which may be an EC-60™ ABSController from Bendix Commercial Vehicle Systems LLC in Elyria, Ohio.The tractor controller 14 communicates with a towed vehicle anti-lockbrake system (ABS) fault indicator 19, located in the cab of the tractor12. The tractor controller 14 is also connected to a power line 15. Thepower line 15 is electrically connected in parallel with each of thetowed vehicles in the combination vehicle 10 through wires of differentlengths and multi-pin connectors on each towed vehicle (not shown).

The combination vehicle 10 further comprises a first trailer, or firsttowed vehicle 20, that is mechanically, electrically and pneumaticallyconnected to the tractor 12. The first towed vehicle 20 includes a firsttowed vehicle controller 22, which may be a TABS-6 Trailer ABS modulefrom Bendix Commercial Vehicle Systems LLC of Elyria Ohio. The firsttowed vehicle controller 22 is housed in an enclosure 28 and controlsABS functions on the first towed vehicle 20. The first towed vehiclecontroller 22 is in electrical communication with the power line 15. Thefirst towed vehicle 20 also includes a first towed vehicle faultindicator 29. The first towed vehicle fault indicator 29 is located in aposition on the first towed vehicle 20 separate from the first towedvehicle controller 22 that may be visible to the driver of the tractor12.

The combination vehicle 10 further comprises a first dolly, or secondtowed vehicle 30, that is mechanically, electrically and pneumaticallyconnected to the first towed vehicle 20. The second towed vehicle 30includes a second towed vehicle controller 32, which may be a TABS-6Trailer ABS module from Bendix Commercial Vehicle Systems LLC of ElyriaOhio. The second towed vehicle controller 32 is housed in an enclosure38 and controls ABS functions on the second towed vehicle 30. The secondtowed vehicle controller 32 is in electrical communication with thepower line 15. The second towed vehicle 30 also includes a second towedvehicle fault indicator 39. The second towed vehicle fault indicator 39is located in a position on the second towed vehicle 30 separate fromthe second towed vehicle controller 32. The position of the second towedvehicle fault indicator 39 may be visible to the driver when he is inthe tractor 12.

The combination vehicle 10 further comprises a second trailer, or thirdtowed vehicle 40, that is mechanically, electrically and pneumaticallyconnected to the second towed vehicle 30. The third towed vehicle 40includes a third towed vehicle controller 42, which may be a TABS-6Trailer ABS module from Bendix Commercial Vehicle Systems LLC of ElyriaOhio. The third towed vehicle controller 42 is housed in an enclosure 48and controls ABS functions on the third towed vehicle 40. The thirdtowed vehicle controller 42 is in electrical communication with thepower line 15. The third towed vehicle 40 also includes a third towedvehicle fault indicator 49. The third towed vehicle fault indicator 49is located in a position on the third towed vehicle 40 separate from thethird towed vehicle controller 42 that may be visible to the driver ofthe tractor 12.

The combination vehicle 10 further comprises a second dolly, or fourthtowed vehicle 50, that is mechanically, electrically and pneumaticallyconnected to the third towed vehicle 40. The fourth towed vehicle 50includes a fourth towed vehicle controller 52, which may be a TABS-6Trailer ABS module from Bendix Commercial Vehicle Systems LLC of ElyriaOhio. The fourth towed vehicle controller 52 is housed in an enclosure58 and controls ABS functions on the fourth towed vehicle 50. The fourthtowed vehicle controller 52 is in electrical communication with thepower line 15 from the tractor 12. The fourth towed vehicle 50 alsoincludes a fourth towed vehicle fault indicator 59. The fourth towedvehicle fault indicator 59 is located in a position on the fourth towedvehicle 50 separate from the fourth towed vehicle controller 52 that maybe visible to the driver of the tractor 12.

The combination vehicle 10 further comprises a third trailer, or fifthtowed vehicle 60, that is mechanically, electrically and pneumaticallyconnected to the fourth towed vehicle 50. The fifth towed vehicle 60includes a fifth towed vehicle controller 62, which may be a TABS-6Trailer ABS module from Bendix Commercial Vehicle Systems LLC of ElyriaOhio. The fifth towed vehicle controller 62 is housed in an enclosure 68and controls ABS functions on the fifth towed vehicle 60. The fifthtowed vehicle controller 62 is in electrical communication with thepower line 15 from the tractor 12. The fifth towed vehicle 60 alsoincludes a fifth towed vehicle fault indicator 69. The fifth towedvehicle fault indicator 69 is located in a position on the fifth towedvehicle 60 separate from the fifth towed vehicle controller 62 that maybe visible to the driver of the tractor 12.

The towed vehicle ABS fault indicator 19 in the tractor 12 is requiredto be illuminated if there is an ABS fault in any one of the towedvehicles 20, 30, 40, 50, 60. The towed vehicle ABS fault indicator 19will indicate any towed vehicle ABS fault to the driver as long as thetractor controller 14 receives a towed vehicle ABS fault communication,as will be described.

FIG. 2 illustrates a view of the representative electrical system of thecombination vehicle 10 shown in FIG. 1. The tractor controller 14includes a communications port 18 for receiving and transmittingmessages. The communications port 18 communicates with the vehiclecommunications bus. In this combination vehicle 10, the vehiclecommunications bus is the power line 15 that is shared with all of thevehicles in the combination vehicle 10. The power line 15 is typicallyconnected to ignition power, which is received from a twelve volt DCbattery (not shown) on the tractor 12 when the tractor 12 is powered onby the driver. The tractor controller 14 includes an output 17 fortransmitting a signal to the towed vehicle ABS fault indicator 19. Thetractor controller 14 includes a processing and memory unit thatexecutes and persistently stores computer-executable instructions forperforming the various methods, functions, protocols, procedures, etc.,described herein. The processing and memory unit may include volatile,non-volatile memory, solid state memory, flash memory, random-accessmemory (RAM), read-only memory (ROM), electronic erasable programmableread-only memory (EEPROM), variants of the foregoing memory types,combinations thereof, and/or any other type(s) of memory suitable forproviding the described functionality and/or storing computer-executableinstructions for execution by the processing unit. The processing andmemory unit includes control logic 16 for receiving messages on thevehicle communications bus via the communications port 18. One type ofmessage received by the tractor controller 14 is an ABS fault messagegenerated by any one of the towed vehicle controllers 22, 32, 42, 52,62.

The first towed vehicle controller 22 includes a communications port 26.The communications port 26 communicates with the power line 15 that isshared with the other vehicles in the combination vehicle 10. The firsttowed vehicle controller 22 also includes an output 27 for transmittinga signal to the first towed vehicle ABS fault indicator 29. The firsttowed vehicle controller 22 includes a processing and memory unit thatexecutes and persistently stores computer-executable instructions forperforming the various methods, functions, protocols, procedures, etc.,described herein. The processing and memory unit may include volatile,non-volatile memory, solid state memory, flash memory, random-accessmemory (RAM), read-only memory (ROM), electronic erasable programmableread-only memory (EEPROM), variants of the foregoing memory types,combinations thereof, and/or any other type(s) of memory suitable forproviding the described functionality and/or storing computer-executableinstructions for execution by the processing unit. The processing andmemory unit includes control logic 24 for determining faults anddetermining a time elapsed since the combination vehicle 10 was poweredon. The control logic 24 is also capable of receiving and transmittingstatus messages and fault messages via the communications port 26 anddetermining a message load on the power line 15. A fault messagetransmitted by the control logic 24 is transmitted at a first period intime.

The second towed vehicle controller 32 includes a communications port36. The communications port 36 communicates with the power line 15 thatis shared with the other vehicles in the combination vehicle 10. Thesecond towed vehicle controller 32 also includes an output 37 fortransmitting a signal to the second towed vehicle ABS fault indicator39. The second towed vehicle controller 32 includes a processing andmemory unit 34 that executes and persistently stores computer-executableinstructions for performing the various methods, functions, protocols,procedures, etc., described herein. The processing and memory unit 34may include volatile, non-volatile memory, solid state memory, flashmemory, random-access memory (RAM), read-only memory (ROM), electronicerasable programmable read-only memory (EEPROM), variants of theforegoing memory types, combinations thereof, and/or any other type(s)of memory suitable for providing the described functionality and/orstoring computer-executable instructions for execution by the processingunit. The processing and memory unit includes control logic 34 fordetermining faults and determining a time elapsed since the combinationvehicle 10 was powered on. The control logic 34 is also capable ofreceiving and transmitting status messages and fault messages via thecommunications port 36 and determining a message load on the power line15. A fault message transmitted by the control logic 34 is transmittedat a second period in time, the second period in time being differentthan the first period in time.

The third towed vehicle controller 42 includes a communications port 46.The communications port 46 communicates with the power line 15 that isshared with the other vehicles in the combination vehicle 10. The thirdtowed vehicle controller 42 also includes an output 47 for transmittinga signal to the third towed vehicle ABS fault indicator 49. The thirdtowed vehicle controller 42 includes a processing and memory unit 44that executes and persistently stores computer-executable instructionsfor performing the various methods, functions, protocols, procedures,etc., described herein. The processing and memory unit 44 may includevolatile, non-volatile memory, solid state memory, flash memory,random-access memory (RAM), read-only memory (ROM), electronic erasableprogrammable read-only memory (EEPROM), variants of the foregoing memorytypes, combinations thereof, and/or any other type(s) of memory suitablefor providing the described functionality and/or storingcomputer-executable instructions for execution by the processing unit.The processing and memory unit includes control logic 44 for determiningfaults and determining a time elapsed since the combination vehicle 10was powered on. The control logic 44 is also capable of receiving andtransmitting status messages and fault messages via the communicationsport 46 and determining a message load on the power line 15. A faultmessage transmitted by the control logic 44 is transmitted at a thirdperiod in time, which is different than the first period in time and thesecond period in time.

The fourth towed vehicle controller 52 includes a communications port56. The communications port 56 communicates with the power line 15 thatis shared with the other vehicles in the combination vehicle 10. Thefourth towed vehicle controller 52 also includes an output 57 fortransmitting a signal to the fourth towed vehicle ABS fault indicator59. The fourth towed vehicle controller 52 includes a processing andmemory unit 54 that executes and persistently stores computer-executableinstructions for performing the various methods, functions, protocols,procedures, etc., described herein. The processing and memory unit 54may include volatile, non-volatile memory, solid state memory, flashmemory, random-access memory (RAM), read-only memory (ROM), electronicerasable programmable read-only memory (EEPROM), variants of theforegoing memory types, combinations thereof, and/or any other type(s)of memory suitable for providing the described functionality and/orstoring computer-executable instructions for execution by the processingunit. The processing and memory unit includes control logic 54 fordetermining faults and determining a time elapsed since the combinationvehicle 10 was powered on. The control logic 54 is also capable ofreceiving and transmitting status messages and fault messages via thecommunications port 56 and determining a message load on the power line15. A fault message transmitted by the control logic 54 is transmittedat a fourth period in time, which is different than the first period intime, second period in time and third period in time.

The fifth towed vehicle controller 62 includes a communications port 66.The communications port 66 communicates with the power line 15 that isshared with the other vehicles in the combination vehicle 10. The fifthtowed vehicle controller 62 also includes an output 67 for transmittinga signal to the fifth towed vehicle ABS fault indicator 69. The fifthtowed vehicle controller 62 includes a processing and memory unit 64that executes and persistently stores computer-executable instructionsfor performing the various methods, functions, protocols, procedures,etc., described herein. The processing and memory unit 64 may includevolatile, non-volatile memory, solid state memory, flash memory,random-access memory (RAM), read-only memory (ROM), electronic erasableprogrammable read-only memory (EEPROM), variants of the foregoing memorytypes, combinations thereof, and/or any other type(s) of memory suitablefor providing the described functionality and/or storingcomputer-executable instructions for execution by the processing unit.The processing and memory unit includes control logic 64 for determiningfaults and determining a time elapsed since the combination vehicle 10was powered on. The control logic 64 is also capable of receiving andtransmitting status messages and fault messages via the communicationsport 66 and determining a message load on the power line 15. A faultmessage transmitted by the control logic 64 is transmitted at a fifthperiod in time, which is different than the first period in time, secondperiod in time, third period in time and fourth period in time.

Accordingly, a first towed vehicle controller comprises an enclosure anda controller in the enclosure. The controller comprises a processor withcontrol logic, the control logic capable of determining at least one ofa status and a fault of the first towed vehicle and transmitting faultmessages and status messages on the vehicle communications bus receivingfault messages and status messages on a vehicle communications bus. Thecontrol logic receives a fault message from a second towed vehiclecontroller on the vehicle communications bus at a second period in timeand transmits the fault message of the second towed vehicle controllerto the vehicle communications bus at a first period in time, which isdifferent than the second period in time.

In accordance with another example, a system for a combination vehiclehaving a plurality of towed vehicles comprises a tractor controller incommunication with a vehicle communications bus; a first towed vehiclecontroller in communication with the vehicle communications bus andcapable of receiving and transmitting messages to the vehiclecommunications bus; and a second towed vehicle controller incommunication with the vehicle communications bus and capable ofreceiving and transmitting messages to the vehicle communications bus ata second period in time. The first towed vehicle controller discontinuestransmitting a status message in response to receiving a fault messagefrom the second towed vehicle controller and starts transmitting thefault message of the second towed vehicle controller to the vehiclecommunications bus at the first period in time, which is different thanthe second period in time.

A flowchart for implementing a method 80 of the present invention isshown in FIG. 3. In step 82, the second towed vehicle control logic 34determines a fault has occurred in the anti-lock brake system of thesecond towed vehicle 30. In step 84, the control logic 34 beginstransmitting a fault message at a second period in time via thecommunications port 36. The fault message is transmitted using abidirectional serial communications protocol, such as SAE J1587Electronic Data Interchange Between Microcomputer Systems in Heavy-DutyVehicle Applications, over the vehicle power line 15 using a physicallayer protocol such as SAE J2497 Power Line Carrier Communications forCommercial Vehicles. The fault message is encoded according to thephysical layer protocol and sent with a certain message frequency, suchas about once every 500 milliseconds, and the resultant signal on thepower line has a specific amplitude, such as about 4V peak to peak. Thefault message is sent continuously as long as a fault is present at thesecond towed vehicle 30. The second towed vehicle control logic 34 alsotransmits a signal to the output 37 to illuminate the fault indicator 39on the second towed vehicle 30.

In step 86, the fault message is received by the first towed vehicle 20at the communications port 26. The fault message transmitted on thepower line 15 may experience attenuation, mainly due to the loading onthe power line 15 from the controllers 22, 32, 42, 52, 62 and otherelectrical equipment on the same power line 15. The signal to noiseratio decreases as the amount of electrical equipment on the power line15 increases. Some attenuation is also due to the length of the powerline, which may be over thirty feet, as well as due to noise orinterference. The fault message amplitude may be degraded by severalvolts from the original amplitude due to any or all of these reasons.However, as long as the fault message meets a predetermined minimumamplitude at the communications port 26, the fault message can bereceived and interpreted by the first towed vehicle control logic 24. Inone example, the predetermined minimum amplitude is about fiftymillivolts peak to peak.

In step 88, the control logic 24 determines if a predetermined timeperiod has elapsed since the power on of the combination vehicle 10. Aspart of a test sequence, each controller 22, 32, 42, 52, 62 sends afault message on the power line 15 immediately upon power on of thecombination vehicle 10 in order to test the towed vehicle ABS faultindicator 19 operation in the tractor 12. The predetermined time periodis set at about one minute to ensure that the fault message received bythe first towed vehicle controller 22 is actually an ABS fault of thesecond towed vehicle controller 32 and not part of the power on test ofABS fault indicator 19. If the predetermined time period has elapsed,the method 80 proceeds to step 90. If the predetermined time period hasnot elapsed, the method 80 returns to step 86 to wait for a faultmessage to be received.

In step 90, the control logic 24 checks whether the first towed vehiclecontroller 22 is transmitting its own status message on the power line15. The first towed vehicle controller 22 may be transmitting a statusmessage over the communications port 26 concerning a state of the firsttowed vehicle 20. Examples of status messages include a door ajar,odometer mileage and tire pressure values. These status messages have alower priority than an ABS fault message. If the control logic 24 istransmitting a status message in step 90, the status message isterminated in step 92 and the method 80 continues to step 94. If thefirst towed vehicle control logic 24 is not transmitting a statusmessage, the method 80 continues directly to step 94.

In step 94, the control logic 24 determines the load, or number ofmessages, currently on the power line 15. If the message load is greaterthan or equal to a predetermined load, the method 80 returns to step 84to wait for fault messages and for the message load to decrease. Inanother embodiment, if the message load is greater than or equal to apredetermined message load, the control logic (24) waits a random amountof time, such as between one and ten message times, before checkingagain if the message load has decreased. In one example, thepredetermined message load is 80%. Factors that contribute to anincreased message load on the power line 15 include other controllersthat may be equipped with the method 80 of this invention that mayalready be repeating the fault message. If the message load is less thanthe predetermined load, the method 80 proceeds to step 96.

In step 96, the first towed vehicle control logic 24 transmits the faultmessage of the second towed vehicle 30 on the power line 15. The firsttowed vehicle control logic 24 does not alter the content of the faultmessage but rather repeats the fault message exactly as it was received.However, the control logic 24 repeats the fault message at a period intime different than the period in time used by the second towed vehiclecontrol logic 34 to originally transmit the fault message. In thismanner, both the fault message transmitted by the first towed vehiclecontrol logic 24 and the fault message transmitted by the second towedvehicle control logic 34 do not interfere with each other on the powerline 15. In addition, when the fault message is repeated by the firsttowed vehicle control logic 24, the fault message amplitude is increasedback to an amplitude value within the specification of the particularcommunications protocol. The effects of noise and power line length arediminished with the repetition of the fault message of the second towedvehicle 30 by the control logic 24 of the first towed vehicle 20.

In step 98, the tractor 12 receives the fault message. The fault messageis likely to be greater than a minimum amplitude due to the repetitionof the fault message by the first towed vehicle control logic 24, whichis located in closer proximity to the tractor 12 than the second towedvehicle 30. In addition, the fault message will be repeated at twodifferent period in times, which increases the number of fault messageson the power line 15. The towed vehicle control logic 16 only needs toreceive one of the fault messages on the power line 15 in order to senda signal to output 17 to illuminate the towed vehicle ABS faultindicator 19 in the tractor 12 in step 96. In this manner, the driverreceives notice of an ABS fault at one of the towed vehicles in thecombination vehicle 10.

Accordingly, a method of communicating a fault in a combination vehiclecomprises receiving and transmitting messages on a vehiclecommunications bus among a first towed vehicle controller; a secondtowed vehicle controller and a tractor controller; transmitting a faultmessage from the second towed vehicle controller to the vehiclecommunications bus at a second period in time; receiving the faultmessage at the first towed vehicle controller on the vehiclecommunications bus; transmitting the fault message by the first towedvehicle controller at a first period in time, which is different thanthe second period in time.

The method described herein improves the transmission and likelihood ofreception of a fault message by the tractor 12. A towed vehiclecontroller proximate to the tractor 12, such as the first towed vehiclecontroller 22, relays fault messages received on the power line 15 froma towed vehicle controller distal to the tractor, such as the secondtowed vehicle controller 32. However, the vehicle controller distal tothe first towed vehicle controller can be any one of the controllers 42,52, 62. In order to clear the fault message on the power line 15, thefault must be fixed on the second towed vehicle 30 and the entirecombination vehicle 10 must undergo a power on cycle.

The method is applicable to a multi-trailer combination vehicle, such asshown in FIG. 1, so that any towed vehicle controller 22, 32, 42, 52, 62is capable of re-transmitting a fault message from another towed vehiclecontroller. When the fifth towed vehicle controller 62 transmits a faultmessage on the power line 15, the degradation of the fault message fromthe fifth towed vehicle controller 62 to the tractor controller 14 couldbe several volts. If the fault message is lower than a predeterminedminimum amplitude, the towed vehicle controller 22 would not receive andinterpret the fault message and illuminate the towed vehicle ABS faultindicator 19. Repetition of the fault message at the amplituderecommended by the particular protocol by any other controller on thevehicle communications bus increases the likelihood of reception of theABS fault message by the towed vehicle.

The number of towed vehicles in a combination vehicle may be as few astwo or greater than five, depending on the configuration. While it iscontemplated that all of the controllers on the combination vehicleinclude the control logic for implementing this invention, the methoddescribed herein will function with a single towed vehicle controllercapable of implementing the method of this invention being the towedvehicle proximate to the towed vehicle, but not necessarily connecteddirectly to the towed vehicle, and any other number or types ofcontrollers in between the controller implementing this invention andthe controller transmitting the fault message.

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. Therefore, the invention, in its broaderaspects, is not limited to the specific details, the representativeapparatus, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of the applicant's general inventive concept.

I claim:
 1. A method of communicating a fault in a combination vehiclecomprising: receiving and transmitting messages on a power line, thepower line operating as a vehicle communications bus wherein themessages are received and transmitted among a first towed vehiclecontroller transmitting messages at a first period in time; a secondtowed vehicle controller transmitting messages at a second period intime and a tractor controller; transmitting a fault message from thesecond towed vehicle controller indicative of a fault in a second towedvehicle to the vehicle communications bus continuously at the secondperiod in time; receiving the fault message at the first towed vehiclecontroller on the vehicle communications bus; terminating thetransmission of a status message of the first towed vehicle controller;transmitting the fault message by the first towed vehicle controllercontinuously at the first period in time, the first period in time beingdifferent than the second period in time; receiving the fault messagetransmitted at the first period in time at the tractor controller; andindicating that a fault exists in the second towed vehicle in responseto receiving the fault message at the tractor controller by illuminatinga visible fault indicator to a driver of a tractor having the tractorcontroller.
 2. The method as in claim 1, further comprising increasingthe fault message amplitude to a minimum value specified by the vehiclecommunications bus as the first towed vehicle controller transmits thefault message.
 3. The method as in claim 1, wherein receiving andtransmitting messages on the vehicle communications bus comprises usinga power line shared among the first towed vehicle controller, the secondtowed vehicle controller and the tractor controller.
 4. The method as inclaim 1, further comprising transmitting the fault message using a SAEJ2497 protocol on the vehicle communications bus.
 5. The method as inclaim 1, further comprising determining a load of the vehiclecommunications bus is less than a predetermined load prior totransmitting the fault message by the first towed vehicle controller. 6.The method as in claim 1, wherein transmitting the fault message by thefirst towed vehicle controller occurs after a predetermined time periodhas elapsed between power on of the tractor controller and the receivingof the fault message by the first towed vehicle controller.